Urea-formaldehyde composition



Patented Mar. 7, 1944 I} Be: P. Cosgrove, Toledo, Ohio,

assignments, Company,

Libbey-Owens-Ford Glass a corporation of Ohio No Drawing. 8 Application February 24, 1943, l

minor, by meme erial No. 476,938 v 3 Claims. The invention relates to a thermosettingcornposition comprising a urea-formaldehyde reaction product and a novel latent accelerator or curing catalyst.

When a thermosetting composition is shaped in a mold under pressure at an elevated temperature, it first softens and then hardens at the molding temperature, whereas a thermoplastic composition remains soft until the molded piece is cooled. As a result, an article can be molded from a thermosetting composition by simply placing the composition in a hot mold, closing the mold, and then removing the finished article after a relatively short time while the mold is still hot. The molding of an article from a thermoplastic compositionpresents a more complex problem, because an article molded from such a composition must be cooled before the mold is opened to prevent blistering and other deformation which would occur if the mold were opened while the thermoplastic material was still hot.

The length of timefor which a molding composition must be left in the mold is one of the factors determining the cost of the articles molded from the composition. A composition that must be left in the mold twice as long as another composition requires about twice as much molding equipment for the same volume of production, and hot-molding equipment is expensive.

A urea-formaldehyde reaction product is thermosetting in the presence of an acid substance in that it is transformed by heat from a fusible composition into an infusible resin. In order to cause such transformation to take place, an acid substance must be present to act as a catalyst. In the molding of an article from a. urea-formaldehyde composition, it is necessary to leave the composition in the hot mold for a short time after the mold has been closed in order to complete the transformation to the infusible resin so as to produce an article of optimum quality. The length of time for which it is necessary to leave a urea-formaldehyde composition in the mold varies with the degree of acidity produced by the acid substance used as a catalyst: the more acid the composition, the shorter the time required to complete the transformation to an infusible resin in the hot mold. There is, of course,

a demand for urea-formaldehyde molding compositions that are completely converted into an infusible resin so that the finished article can be removed from the mold a relatively short time after the mold has been closed.

In spite of the advantage of acidity during the molding of a urea-formaldehyde composition, a

urea-formaldehyde molding composition cannot be supplied in an acid condition by a manufacturer, because a urea-formaldehyde composition that is acid is unstable in storage. If it is acid,

a urea-formaldehyde composition gradually becomes lniusible at ordinary temperatures. Such a composition could not be sold by a manufacturer because it would be infusible and worthless by the time it reached the hands of a molder.

Even slight acidity which causes the composition to become infusible very gradually would make the composition commercially unacceptable, because the plasticity and other molding properties of such a composition would be wholly dependent upon the atmospheric temperature prevailing and the number of hours elapsed between the production of the finished composition by the manufacturer and the molding of the composition by the user. A manufacturer who molds articles from a urea-formaldehyde composition must select a composition of the proper plasticity and test the composition by molding it under various conditions to' determine the exact conditions required to give the desired results. In order to maintain the quality of the product, he must then continue to use a composition of exactly the same plasticity and must mold it under exactly the same conditions. If the composition used by the molder is unstable and has molding properties which vary with the length of time elapsed since the composition was produced, it is impossible for the molder to mold successive batches of the composition under the conditions required to give satisfactory results.

A latent accelerator in a urea-formaldehyde composition is an ingredient that accelerates the transformation of the composition to an infusible resin in a hot mold, but does not materially impair the stability of the composition in storage at ordinary temperatures prior to hot molding. True latent accelerators are very rare. A latent accelerator may be alkaline, neutral or so slightly acid that it does not appreciably acidity a ureaformaldehyde composition when added thereto. It is believed that such a substance breaks up or undergoes molecular rearrangement to form an acid, but does not do so until the molding temperature is reached. Such a substance does not act as an accelerator unless the acid so formed is strong enough to serve as a catalyst to cause the transformation of the urea-formaldehyde reaction product into an infusible resin.

A urea-=formaldehyde molding composition contains an appreciable amount of moisture and frequently is kept in storage for weeks at a time before being used. Many substances that might be expected to decompose to form acids under molding conditions suifer the same decomposition within a few hours after being intimately mixed with a urea-formaldehyde composition, and therefore are not latent accelerators Moreover, the

behavior of a substance when present as a minor ingredient in a molding composition and subiected to molding pressure at the molding temperature of 270-to 330 F. cannot be predicted from its behavior when subjected by itself to such a temperature under atmospheric pressure. Most of the potentially acid substances that do not impair the stability of amolding composition when incorporated therewith fail to accelerate the transformation of the composition to an infusible resin in a hot mold.

Although certain halogenated organic compounds that liberate hydrobromic or hydrochloric acid when heated have been known to act as latent accelerators when incorporated in ureaformaldehyde molding compositions, accelerators that liberate organic acids are preferable to accelerators that liberate strong inorganic acids, because of the danger of mold corrosion by strong inorganic acids. Certain organic peroxides, such as benzoyl peroxide, have been used heretofore as latent accelerators, but there are many organic pigments useful in molding compositions that are deleteriously affected when a peroxide is present in the composition.

The principal object of the inventioh is to provide a thermosetting urea-formaldehyde composition containing a novel latent accelerator. More specific objects and advantages are apparent from the description, which discloses and illustrates the invention, and is not intended to impose limitations upon the claims.

A thermosetting composition embodying the invention comprises a urea-formaldehyde reaction product and o-sulfamido methyl benzoate I c o-cn;

as a latent accelerator.

In the preparation of a reaction product of urea and formaldehyde for use in a composition embodying the invention, the urea may be re- =acted with either formaldehyde or a polymer sired base such as sodium or potassium hydroxide or any weaker base, or an organic base such as triethanolamine may be employed. The preferred proportion is 3 mols of formaldehyde for 2 mols of urea. Approximately 2 mols of formaldehyde are all that will react with each mol of urea, but anexcess of formaldehyde above such maximum or a smaller proportion ranging down to about 1 mol of formaldehyde for each mol of urea may be used for the reaction if desired. Because of the complexity of the molecules of the reaction products that are produced, the proportion of formaldehyde actually reacting with the urea may vary freely between the limits stated. The reaction proceeds at ordinary temperatures, but heat may be used to shorten the time of reaction if desired. A reaction product may be prepared by carrying the reaction of the any further stage at which the reaction productis still fusible.

The preferred method of preparing a molding composition consists in preparing an aqueous solution of a urea-formaldehyde reaction product, then impregnating cellulosic material with the solution and drying. Although alpha cellulose is the purest and lightest-colored cellulosic material that may be employed, any other cellulosic material, such as wood flour, wood pulp, newsprint, printed newspaper, sawdust, shavings, walnut shell flour, or ground corn cobs may be employed. The impregnated and dried cellulosic material is preferably ground to a line powder in order to produce a homogeneous composition, and the latent accelerator is preferably incorporated during such grinding stage. The customary modifiers such as hot-plate lubricants, opacifiers, pigments and other coloring matter may also be incorporated during the grinding. The fine powder so obtained may be formed into coarse granules, or into solid blanks or pre forms of the proper sizes for use in various molds. Molded articles may be produced in the usual manner by compressing the composition in a closed mold under a pressure of l to 4 tons per square inch of projected area and at a temperature of 270-330 F. The proportion of cellulosic material in a dry composition embodying the invention is preferably from about 30 to about 40 per cent, but may range from 0 per cent to as much as 60 per cent in the case of a dense cellulosic material, such as walnut shell flour. The proportion of the latent accelerator employed is simply that proportion which causes the hardening to take place at the desired speed.

Example After alpha cellulose fiber (80 parts by weight) has been impregnated with an aqueous solution containing 120 parts of a urea-formaldehyde reaction product, the impregnated material is dried by any of the usual drying methods. Heat may be used as is customary to expedite the drying, and drying by means of a stream of air is convenient. The dried material is ground in a ball mill together with from about to about 1 per cent of its weight of o-sulfamido methyl benzoate and any other desired modifiers. The

product is usable as a molding composition for many applications but can be granulated or preformed. Various compositions embodying the invention may be prepared to meet various requirements.

Having described my invention, I claim:

1. A thermosetting composition comprising a urea-formaldehyde reaction product and o-sulfamido methyl benzoate as a latent accelerator.

2. A thermosetting composition comprising a urea-formaldehyde reaction product, cellulosic material, and o-sulfamido methyl benzoate as a latent accelerator.

3. A thermosetting composition comprising a urea-formaldehyde reaction product and about one per cent of o-sulfamido methyl benzoate as a latent accelerator.

REX P. COSGROVE 

